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A Dam Impressive Feat

The race is on to finish repairing the Oroville spillway before the rainy season returns.

SLIDESHOW

Crews place rebar panels for new sidewalls and structural concrete on the upper chute of the damaged Oroville Dam spillway.

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The damaged lower portion of the spillway, as seen in February.

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Randy Mills vacuums out debris before structural concrete is placed on the lower chute of the spillway.

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Jozef Karmmer uses a plumb line to survey the location for a stay form on the upper chute of the spillway.

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It is, in the words of one spokesperson, “one of those you’re-building-the-airplane- on-the-way-down things”: a mad, make-or-break, everybody-in-the-pool race against Mother Nature. It is the repair of the spillway to the 770-foot-tall Oroville Dam, which last winter began to crumble, threatening to loose a 30-foot wall of water on Butte and Yuba Counties.

Now crews are working around the clock trying to restore the dam’s massive, half-mile-long spillway before the wet season begins again this winter—and to combat what climate experts expect to be more frequent, and intense, rainstorms. That’s meant a fly-by-the-seat-of-your-pants rebuild. Crews from Kiewit Corporation, the California Department of Water Resources (DWR), and other subcontractors started construction on the dam while plans were only 30 percent done—a process known as “design build” that’s practically unheard of for an infrastructure project of this scale. A crew of 600 has been working in shifts 24-7 on the damaged lower portion of the dam’s spillway, pouring 800,000 cubic yards of concrete. An onsite concrete plant refills trucks every five minutes. Says Jeff Petersen, the project director with Kiewit, “The Oroville spillways repair project is one of the most challenging projects we’ve ever been involved in.”

All told, Kiewit’s crew will log 600,000 man-hours by November 1, the date by which the main spillway, which acts as the first line of defense when the dam overflows, must be repaired or patched, as the risk of winter rains bringing the dam to maximum capacity begins to rise. As part of the repairs, sections of the lower and upper spillway are being reinforced with 146,000 cubic yards of structural concrete for added security. That’s enough to lay down a six-foot-wide sidewalk that stretches from Sacramento to Los Angeles.

The project’s rushed timeline even stuns experts. “This is basically a half-billion-dollar construction project, and they got it started within months,” says Jay Lund, director of the Center for Watershed Sciences at UC Davis. “Normally it would take years, even decades, to organize permits, get out contracts, and go through all the post-bid bureaucracy. It’s quite a feat.”

Once finished, the spillway will include a new cutoff wall for extra security. For now, the DWR has dropped the water level in Lake Oroville to make room for rains. Hopefully, that buys enough time for the cement to dry on a truly massive project. And while there’s no indication that Northern California’s wet season will bring anywhere near last year’s record downfall, if we’ve learned anything from Oroville, it’s that there’s nothing wrong with an abundance of caution.